1. Field of the Invention
This invention relates to a crystallization apparatus and method for a semiconductor device, and more particularly to a crystallization apparatus and method for crystallizing a semiconductor using the non-vacuum process.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls the light transmissivity of liquid crystal cells in accordance with video signals to display a picture corresponding to the video signals on a liquid crystal panel having the liquid crystal cells arranged in a matrix type. Such a LCD has used thin film transistors (TFTs) as switching devices for selecting pixel cells.
The TFT is classified into an amorphous silicon type and a poly silicon type depending upon whether a semiconductor layer is made from amorphous silicon or poly silicon. The amorphous silicon-type TFT has advantages of a relatively good uniformity and a stable character, whereas it has a drawback of low charge mobility. Also, it has a drawback in that, when the amorphous silicon-type TFT is used, peripheral driving circuits must be mounted onto a display panel after they were separately prepared. On the other hand, the poly silicon-type TFT has an advantage in that, since it has high charge mobility, it is easy to increase the pixel density and peripheral driving circuits can be directly mounted onto a display panel.
The formation of the poly silicon-type TFT is followed by a process of crystallizing an amorphous silicon substrate. In the crystallization process, a laser beam is irradiated mainly within a vacuum chamber so as to reduce a grain boundary.
Referring to FIG. 1 and FIG. 2, there is shown a conventional crystallization apparatus that includes a loadlock chamber 2 loaded with a glass substrate 9, a vacuum chamber 6 for crystallizing the glass substrate 9, and a transfer chamber 8 provided between the loadlock chamber 2 and the vacuum chamber to transfer a glass. A plurality of glass substrates 9 having been cleaned and dried is disposed within the loadlock chamber 2. The transfer chamber 8 is provided with a robot arm 4 that is rotary-driven to transfer the glass substrate 9. The vacuum chamber 6 irradiates laser beams onto the glass substrate 9 to crystallize it. The crystallization process will be described below. The glass substrate 9 transferred into the vacuum chamber 6 by means of the robot arm 4 and safely loaded on a stage 7 is provided with an amorphous semiconductor layer. Laser beams irradiated within the vacuum chamber 6 has a beam profile with Gaussian distribution characteristic as shown in FIG. 3, and are irradiated with being overlapped for the purpose of making a fair laser irradiation. When such laser beams are irradiated onto the glass substrate 9, the glass substrate 9 is changed into a polycrystalline structure by growing grains different in crystalline orientation from the lower surface of the glass substrate 9 while heating it by the laser beams and thereafter cooling it.
In the conventional crystallization apparatus, however, as grains different in crystalline orientation are exploded while the glass substrate 9 is heated by laser beams and then cooled, grain boundaries 9a are protruded between the grains as shown in FIG. 4. Assuming that a thickness of an amorphous semiconductor layer in the glass substrate 9 is 500 xc3x85, the grain boundary 9a is protruded into a height of about xc2x1100 xc3x85. Such a grain boundary 9a not only causes the generation of a short between electrodes in the course of the process or upon completion of the TFT, but also it causes a crack of the glass substrate 9 by a thermal or physical impact. Accordingly, the crystallization is made within the vacuum chamber 6 maintaining a high vacuum degree so as to reduce the number of grain boundaries 9a or the protruded height of the grain boundaries 9a , but the grain boundaries 9a are not restrained at a satisfying level. Also, the crystallization apparatus of FIG. 1 and FIG. 2 has problems in that it may be contaminated in a process of transferring the glass substrate 9 by means of the robot arm 4, and that it is difficult to manage the vacuum degree of each chamber and it undergoes an excessive time waste whenever the glass substrate 9 is transferred by means of the robot arm 4. In other words, in FIG. 1 and FIG. 2, when the glass substrate 9 within the loadlock chamber 2 is moved into the transfer chamber 8, a gate valve 3 between the loadlock chamber 2 and the transfer chamber is opened or closed. When the glass substrate 9 is transferred into the vacuum chamber 6 by means of the robot arm 4, a gate valve between the transfer chamber 8 and the vacuum chamber 6 is opened or closed. The conventional crystallization apparatus requires a process of extracting an air from each chamber 2, 6 and 8 so as to keep the vacuum degree within each chamber 2, 6 and 8, particularly within the vacuum chamber 6 after each gate valve 3 and 5 was opened. The throughput is deteriorated due to such an opening or closing operation and such a vacuum degree management of the gate valves 3 and 5.
Accordingly, it is an object of the present invention to provide a crystallization apparatus and method using a non-vacuum process that is adapted to crystallize a semiconductor in a non-vacuum state.
A further object of the present invention is to provide to a crystallization apparatus and method using a non-vacuum process that is adapted to restrain grain boundaries.
In order to achieve these and other objects of the invention, a crystallization apparatus using a non-vacuum according to one aspect of the present invention includes crystallizing means for irradiating laser beams onto a substrate to grow a crystal unilaterally from the side surface of the substrate.
A crystallization method using a non-vacuum according to another aspect of the present invention includes the steps of irradiating laser beams onto a substrate to grow a crystal unilaterally from the side surface of the substrate.